This invention relates to the working of fine wires, and, more particularly, to an apparatus for cold welding of small diameter wire.
Small diameter wire is widely used, especially in electronic circuitry. For example, an integrated circuit ("IC") may make use of wire between 0.025 mm and 0.25 mm in diameter. Though in wide use, such wires are hard to work. In particular, to join one coil to another in order to make a continuous conductor becomes extremely difficult.
Apparatus for cold welding (strictly speaking, forging) of such wire is known, e.g., U.S. Pat. No. 3,680,761. The process consists of placing an end of one fine wire against an end of another fine wire. By great force exerted precisely along the wires' length, the two wires are joined together into a single wire without any overlap.
In conventional cold wire welding apparatus, pairs of dies mounted in blocks selectively grip the wire ends and upset them to form the weld. Each die contains a groove. A pair of grooves act together, when the pair of dies is closed, to form a wire receiving cavity, within which the wire ends are brought together and joined.
The conventional apparatus uses four independent die blocks arranged in pairs. Each pair of blocks grips a wire end. The pairs are forced together in a machine.
The conventional apparatus is single-motion, relying on moving the dies to a common center to insure a tight weld. This apparatus distributes the forces between gripping and upsetting (that is, joining) the two wires.
Great force is necessary to effect a weld, so friction is high. Thus the blocks may move erratically and not come together at the same time. Hence, in the conventional apparatus, the wire ends may not be matched properly to effect a weld. Buckling of the fine wire is also a problem.
One way to overcome the problems of mismatch is to use springs, especially springs that are stronger in one direction than the other. The springs help to smooth the action as the dies move back and forth to weld the wire and then release it without damage.
The conventional apparatus uses a single cycle for welding fine wire. The cycle has three steps: (1) forward-grip wires, (2) upset-reverse-unupset wires, and (3) ungrip wires. Unfortunately, in this single cycle fine wire will break at the unupset position because of friction.